The present invention relates to a package for a semiconductor device, and, more particularly, to a protective package for a spatial light modulator ("SLM") which includes an array of active sites, each of which, in turn, includes a deflectable, light-reflecting beam and address circuitry for selectively deflecting the beam.
Numerous processes are known for producing active sites on a first surface of semiconductor wafers. The active sites may comprise one or more transistors and may include an integrated circuit having a variety of other circuit components. Wafers are ultimately separated into a plurality of individual chips, also known as dies or bars, each of which includes an array of active sites and a surface comprising a portion of what was formerly the wafer's first surface. Each active site has associated therewith one or more bond pads on the first surface. The bond pads are rendered electrically continuous with the active site, typically by depositing or otherwise forming the bond pads on top of, and in electrical contact with conductors formed on the wafer. Often some of the same steps used to produce the active sites also produce the conductors, which are themselves electrically continuous with the active sites.
The separation of the wafer into individual chips is produced by an operation which may be referred to as "sawing." Sawing separates the wafer along lines or paths extending between locations whereat adjacent active sites reside or will ultimately reside.
Wafers are often sawed into chips before effecting the processing which produces the active sites. The resulting chips are maintained in a chip matrix after sawing, and the chip matrix is processed to produce the active sites on each one thereof. The active sites may include or be associated with a spatial light modulator ("SLM"), such as that known as a deflectable mirror device or a digital micromirror device (collectively "DMD").
A DMD includes a light-reflective beam or similar mechanical member, which is associated with an active site and is so mounted to, or hinged from, the material of the wafer and the resulting chip as to be deflectable or movable between a normal position and one or more other positions. Deflection of the beam is achieved by attracting the beam toward or to an adjacent electrode which is at a different electrical potential from that of the beam. Deflection of the beam stores energy in the mount or hinge, which stored energy tends to return the beam to its normal position. Movement of the beam, which may be binary or analog, is controlled by the circuit components of the active sites associated with the beams. Deflection of the beam is facilitated by an undercut well which underlies the beam. The well is formed by appropriate etching of the wafer/chip material.
In use, an array or matrix of DMD's is arranged to receive light from a source. The received light which is incident on the reflective beams is selectively reflected or not reflected onto a viewing surface depending on the position of the beam. Such reflected light may be directed by each beam onto the viewing surface only when it is in one of its possible positions. In all other positions of each beam, the incident, reflected light is directed in such a way that it does not fall on the viewing surface. Appropriate energization of the circuit components associated with each beam of each active site permits the beam-reflected light on the surface to be presented as a rasterized array of pixels (as in a typical television) or as a scanning line of pixels (as in a line printer).
Because a DMD includes both circuit components, as well as a microminiature deflectable beam, it is especially sensitive to the environment and is, accordingly, typically sealed in a package which permits light to reach and to be reflected from the beams of the array. The package is desirably inexpensive to manufacture and to emplace and should not adversely affect the operation of the associated DMD's. Moreover, as noted above, unmodulated light is not reflected by the beams to a viewing surface. However, unless care is taken to properly "handle" this unmodulated light its reflection and/or absorption by surfaces in and surrounding the DMD may cause it to act as though it was modulated and to reach the viewing surface. As a consequence, it is also desirable if a DMD package also prevented, or aided in preventing, unmodulated light from reaching the viewing surface.
Accomplishing the above desiderata is one of the objects of the present invention.